Process of reducing the cadmium content of zinc ore



Nov. 13, 1928. 1,691,714

0. GERLACH ET AL PROCESS OF -I {EIDUCII J(.T THE CADMIUM CONTENT OF ZINCORE Filed Dec. 5, 1926 Patented Nov. 13, 1928 UNITED. STATES A 1,691,714TENT OFFICE.

OSCAR GERLACH, 0F PERU, AND .NILS OSTMAN, O F LA SALLE, ILLINOIS,ASSIGNORS TO MATTHIESSEN. & HEGELER ZINC 00., OF LA SALLE, ILLINOIS, ACORPORATIONOF ILLINOIS.

PROCESS OF REDUCING THE OADMIUM CONTENT OFZI'NC OIRCE.

Application filed December 3, 1926. 2 Serial Ito. 152,376.

It is the object of the present invention to reduce the content ofcadmium in zinc ore prior to the processing of the ore for zinc in orderthat the spelter when obtained 6 may not contain objectionablequantities of cadmium. With this object in view the ore at a suitablyhigh temperature is subjected to the action of steam in the presence ofa carbonaceous material or carbon. We be- 10 lieve the action to be thatthe steam reacting with the carbon present forms carbon monoxide gas andhydrogen which, at the temperatures employed, reduced the cadmium to themetallic state in which it is vaporized and so removed from the ore. Theinvention is aplicable to sulphide, oxide, carbonate and silicate oresof zinc. In the case of sulphides, the process may be used after the orehas been roasted. Preferably, and as a matter of heat economy, the oreis treated while still hot from the roast. It may be transferreddirectly from the roasting furnaee to a chamber in which it is subjectedto the cadmium reducing process. Before it is fed into said chamber itmay be mixed with coal or other carbonaceous matters. Preferably,however, it is charged into the reducing chamber without such admixtureand then sprayed with oil, which may be petroleum or a product thereof.The hydrocarbons of the oil are, of course, broken up at thetemperatures employed and carbon deposited. Steam is introduced eitherat the same time with or imediately after the oil and is reduced by thecarbon from the oil forming hydrogen and carbon monoxide which, togetherwith the gases from the oil, form the reducing agents which act upon thecadmium present in the ore.

The temperature maintained in the reducing chamber is preferably betweenabout l500 and 1800 F. or even somewhat higher. It is desirable,however, not to employ too high temperatures as to do so would result inthe removal of unnecessarily large quantities of the zinc from the ore.Even at the temperatures given there is a loss of a little zinc but theloss is'not serious in view of the superior metal obtained by reason ofthe removal of cadmium. The latter reduces and volatilizes at somewhatlower temperatures than zinc and even below the temperatures which weemploy and at which zinc is also reduced. But by the introduction ofbeing, say,

steam, as described, and limitation of the amount of reducing agentintroduced, there is a selective. removal of cadmium rather In thedrawingaccompanying and form- I ing a part of this specification we haveshown an apparatus in'which our process may be carried out, though it isto be understood that the invention is independent of the particularapparatus employed. In said drawing, Figure 1 is a longitudinal verticalsection showing a part of a furnace of the well known Hegeler ,typ'emodified for the practice of our process, and Figfl, a transversesection through a part thereof on the plane of the line 2-2 of Fig. 1.

The upper chambers a, I), a, of the furnace are used for roasting theores in the usual manner. The lowermost roasting chamber a communicateswith the; reducing chamber d by means of the chute or. passage e,through which the ore falls after the roasting is finished. The ore israbbled or raked through the chamber a? in which a bed or body of ore ismaintained on the hearth with an ample gas space thereover. Steam isintroduced through a pipe f and oil through a pipe 9. The usual finesare provided for leading away the gases and fumes from the roasting'andreducing chambers but preferably a separate fine is provided for thereducing chamber. In order to maintain a reducing atmosphere in chamber(2 it is necessary that it be substantially closed off from chamher 0but this may be accomplished by maintaining a suflicient depth of ore inpassage e as shown in Fig. 1.

Preferably a somewhat higher temperature is maintained in the reducingchamber than in the roasting chambers, the excess from one hundred toone hundred and fifty degrees. This may be accomplished by means ofexternally applied heat in the usual manner. Ordinarily, however, and inour actual practice of the invention, the partial combustion of the oiland carbon by oxygen furnished by the ore and air leakage is sufiicientto maintain the desired temperature. v

- As an example of the actual practice of ourinvention on a roasted orecontaining 0.4% to 0.5% of cadmium and about 70% zinc, we have treatedthirty seven to forty tons of ore per twenty four hours at a temperatureof about 1800 F. using five to ei ht gallons of oil per hour, with theresult t at the cadmium was substantially driven off with an unimportantloss of zinc.

We claim:

1. A process of removing cadmium from oxygen-containing zinc ore whichcomprises subjecting the ore to steam and an amount of reducing agentsuflicient to reduce the cadmium but not a material part of the zinccontained in the ore at a temperature at which both cadmium and zincreduce.

2, A process of removing cadmium from oxygen-containing zinc ore whichcomprises maintaining the ore at a temperature at which cadmium willreduce from its ox gen and treating itwhile so maintained wit 1 oil andsteam. I

3. A process of'removing cadmium from oxygen-containing zinc ore whichcomprises maintaining the ore at a temperature of about 1800 F. andtreating it with steam and a reducing agent. a

4. A process of removing cadmium from oxygen-containing zinc ore whichcomprises maintaining the ore at a temperature of about 1800 F. andtreating it with steam and oil.

5. A process ofremoving cadmium from oxygen-containing z'inc ore whichconsists in maintaining the ore at a temperature at which cadmium oxidein the presence of a reducing agent will reduce, spraying it with oiland supplying steam. Y

6. A process of removing cadmium from oxygen-containing zinc ore whichcomprises maintaining the ore at a temperature of about 1800 degrees F.,supplying steam to the ore and spraying the ore with oil.

OSCAR GERLACH. NILS OSTMAN.

